The causes of past changes in the global methane cycle and especially the role of marine methane hydrate (clathrate) destabilization events are a matter of debate. Here we present evidence from the North Greenland Ice Core Project ice core based on the hydrogen isotopic composition of methane [dD(CH4)] that clathrates did not cause atmospheric methane concentration to rise at the onset of Dansgaard-Oeschger (DO) events 7 and 8. Box modeling supports boreal wetland emissions as the most likely explanation for the interstadial increase. Moreover, our data show that dD(CH4) dropped 500 years before the onset of DO 8, with CH4 concentration rising only slightly. This can be explained by an early climate response of boreal wetlands, which carry the strongly depleted isotopic signature of high-latitude precipitation at that time.

Uncertainty for dD of CH4 is 3.4 per mil as derived from standard measurements as described in: Bock, M. et al., 2010, doi:10.1002/rcm.4429

Please note, that the concentration data given here have a higher error (of 29 ppbv 1-sigma) compared to conventional methods due to the uncertainty of total air content determination of the dD isotope system.